Flagging devices of various types have been known and used in the metalworking art, particularly the metal grinding art, for some time. A flagging device is an apparatus attached to a machine tool in a fixed position relative to the work space and having a probe extending into the work space to establish a location in the work space to which a reference surface of a workpiece is brought relative to a tool for shaping the workpiece (e.g. a grinding wheel for grinding a metallic workpiece). Among the flagging devices that have been used in the art are those having a probe linked to a dial gage fixed to the machine. The reference surface is brought into contact with the probe, usually manually, and displaces the probe slightly until the needle on the dial gage registers a fixed predetermined value (e.g. zero). This type of flagging device is usually employed with a manually operated machine tool to move the workpiece into position for shaping by a tool. Other flagging devices used in the art employ a probe extending into the work space of a machine tool, that engages mechanically operated electrical switches. In such devices the probe is contacted and slightly displaced by the reference surface of a supported workpiece that has been moved into the probe contacting position by a power driven workpiece carrying member of the machine tool, e.g. machine tool table or movable headstock. The displaced probe manipulates a mechanically operated electrical switch to cause the termination of the linear movement of the workpiece in the work space and thereby positions the workpiece in the work space for engagement by a tool to subsequently shape the workpiece (e.g. by grinding).
Some flagging devices in the art are fixed with respect to the direction of approach of and contact by the reference surface on the probe. Thus the approach may be from the left to the probe, left flagging, or from the right to the probe, right flagging. Still other flagging devices in the art may be switched from one flagging direction (e.g. left flagging) to the opposite flagging direction (e.g. right flagging). Such changes in flagging direction have involved mechanical and/or electrical rearrangements in the flagging device.
Advantageously flagging devices are used in production set ups to reproducably position workpieces of the same shape in a work space of a machine tool for the same shaping operation (e.g. grinding of shoulders or flanges). Although being advantageous for the reproducable positioning of workpieces in the work space of a machine tool, flagging devices using mechanically operated electrical switches are known to be troublesome because the moving mechanical elements of the switch are susceptible to rapid wear and malfunction and the switch is very difficult to seal against liquids, dirt and metal particles from the metal working operation. Such wear and sealing problems result in switch malfunctions and leads to a short life time for the switch and hence to failures and poor performance of the flagging device. Failure or poor operation of the flagging device often leads to machine wrecks where the tool (e.g. grinding wheel) advances to engage the workpiece at a wrong position on the workpiece. It is therefore highly desirable to have a flagging device which overcomes such difficulties and deficiencies.
It is the general object of this invention to provide a bidirectional, reliable, durable flagging apparatus, for positioning a workpiece in a machine tool work space with respect to a tool, that is highly resistant to switch malfunctions due to mechanical deterioration of the switch and the failure of a sealing means for protecting the switch against penetration by liquids, dirt and metal particles. A further object of this invention is to provide a flagging apparatus that is operable in either of two opposing directions for positioning a workpiece in a machine tool work space without the mechanical and/or electrical alteration of the flagging apparatus being required.